1. Field of the Invention
The present invention relates to a sheet sorter that can be employed in an image forming apparatus such as a printer, a copier, and a multifunction device, and to an image forming apparatus equipped with the sheet sorter.
2. Discussion of the Background
Conventionally known sheet sorters sort sheets of recording paper or the like, which are loaded onto a sheet discharge tray from a sheet conveyance unit that conveys the sheets, by shifting the sheet conveyance unit along the sheet plane and in a shift direction orthogonal to the conveyance direction of the sheets (for example, see JP3-42460A).
This sort of sheet sorter has the following disadvantage. With various types of sheets that are used, sheet conditions such as curling may result depending on the characteristics of the type of sheet. This can cause degradation of the stackability of the sheets when discharged onto the sheet discharge tray, meaning that there is a lack of uniformity in the sheets on the sheet discharge tray. Hence, it is not possible to reliably sort the sheets by differentiating between stacks of these sheets (offset sorting).
Furthermore, with a view to improving the stackability of sheets that are discharged onto the sheet discharge tray, it is conventionally known practice to provide a sheet pressing guide to contact the top face of the sheets that are loaded on the sheet discharge tray so as to press the sheets (for example, see JP8-119520A, JP9-77339A, and JP2002-211814A).
More specifically, JP8-119520A discloses that a contact portion of the paper press, which makes contact with the body of the discharge paper tray, is positioned such that only large-size discharged paper is held down.
Furthermore, JP9-77339A discloses a paper storage auxiliary mechanism that includes a first swinging member that makes contact with the forward end of the discharged paper to guide the discharged paper; and a second swinging member that has its one end swingably arranged at the other end of the first swinging member to hold down the paper that has been stacked on the discharge tray.
Furthermore, JP2002-211814A discloses a pair of guides rotationally movable in the vertical direction. One of the guide members is disposed in a dangling manner closer to the original discharge source than the other guide member, so that both guide members can press documents on the original discharge area at different positions.
As reflected in such related art, the following disadvantages are found in sheet sorters that shift a sheet conveyance unit, which conveys sheets, in a shift direction in sorting the sheets loaded onto a sheet discharge tray by the sheet conveyance unit, in cases where sheet pressing guides are provided to press the sheets loaded on the sheet discharge tray by contacting the top face of the sheets.
In such sheet sorters, in conjunction with the sheet conveyance unit moving in the shift direction, the sheet pressing guide moves together with the sheet conveyance unit (specifically, the sheet pressing guide is disposed on the sheet conveyance unit). When the sheet pressing guide comes into contact with the top face of the sheets loaded on the sheet discharge tray, this can lead to a situation in which, when the sheet conveyance unit shifts in the shift direction, the stacks of sheets stacked on the sheet discharge tray slip in the shift direction. This can disturb the offset sorting of the stacks of sheets.
FIGS. 15A to 15C are schematic side views, seen from a shift direction X, of a conventional sheet sorter in which a sheet pressing guide C1 is disposed on a sheet conveyance unit C2 and contacts a top face Pa of sheets P stacked on a sheet discharge tray C3. FIG. 15A shows a situation in which no sheets P are loaded on the sheet discharge tray C3. FIG. 15B shows a situation in which B5 size sheets P are stacked on the sheet discharge tray C3. FIG. 15C shows a situation in which A4 size sheets P are stacked on the sheet discharge tray C3.
FIGS. 16A to 16C are schematic side views, seen from a conveyance direction Y1, of the conventional sheet sorter in which the sheet pressing guide C1 is disposed on the sheet conveyance unit C2 and contacts the top face Pa of the sheets P stacked on a sheet discharge tray C3. FIG. 16A shows a situation in which no sheets P are loaded on the sheet discharge tray C3. FIG. 16B shows a situation in which the sheets P are stacked on the sheet discharge tray C3. FIG. 16C shows a situation in which the sheet conveyance unit C2 shifts in the shift direction X, causing the stack of sheets P stacked on the sheet discharge tray C3 to slip in the shift direction X, so that the offset sorting of the stacks of sheets P is disturbed.
With the conventional sheet sorter shown in FIGS. 15A to 15C and 16A to 16C, the sheet pressing guide C1 is disposed on the sheet conveyance unit C2, above the discharge opening C2a (see FIG. 15A and FIG. 16A), in the center of the sheet conveyance unit C2 in the shift direction X. This allows the sheet pressing guide C1 to move together with the sheet conveyance unit C2 in conjunction with movement of the sheet conveyance unit C2 in the shift direction X. Specifically, the sheet pressing guide C1 is rotationally movable, relative to the sheet conveyance unit C2, about an axis extending in the shift direction X, with the forward end of the sheet pressing guide C1 dangling toward the sheet discharge tray C3 under the weight of the sheet pressing guide C1 itself. Thus, the sheet pressing guide C1 contacts the top face Pa of the sheets P that are loaded on the sheet discharge tray C3, and holds down these sheets P.
For this reason, as shown in FIG. 16C, when the sheet pressing guide C1 moves together with the sheet conveyance unit C2 in conjunction with the sheet conveyance unit C2 moving in the shift direction X, this can lead to a situation in which, due to the contact between the sheet pressing guide C1 and the top face Pa of the sheets P loaded on the sheet discharge tray C3, the stacks of sheets P that are stacked on the sheet discharge tray C3 slip in the shift direction X, which can disturb the offset sorting of the stacks of sheets P.
It is an object of the present invention to provide a sheet sorter and an image forming apparatus equipped with the sheet sorter, which is capable of preventing disturbance of the offset sorting of stacks of sheets, even in cases where the sheet pressing guide moves together with the sheet conveyance unit in conjunction with the sheet conveyance unit moving in the shift direction, by preventing the movement in the shift direction of the stacks of sheets stacked on the sheet discharge tray.